Method for Detecting Misalignment of a Vehicle Headlight Using a Camera

ABSTRACT

A method for detecting misalignment of a vehicle headlight using a camera system is specified. For this purpose, the headlight is in a predefined position and the camera system is arranged on or in the vehicle and is oriented in such a manner that the light distribution pattern of the headlight in front of the motor vehicle is detected. With a predefined headlight position, an actual light distribution pattern of the headlight is recorded using the camera system and is compared with a desired light distribution pattern for the predefined headlight position. If the actual light distribution pattern differs from the desired light distribution pattern, misalignment of the headlight is detected.

The invention relates to a method for detecting misalignment of avehicle headlight and prevents the unintentional dazzling of other roadusers.

The invention introduced here is applied in any vehicle with a camerasystem which detects the environment in front of the vehicle and acontrol unit for the headlight.

Modern adaptive headlight systems such as e.g. high beam assistants witha gliding headlight range adapt to the current traffic conditions bychanging the illumination characteristic. A camera is used in suchsystems to detect preceding and forthcoming vehicles and to determinetheir position. By means of this information the headlight can then beadjusted such that a maximum illumination takes place without dazzlingthe other road users. However, a misaligned headlight can lead to anunintentional dazzling, as not the predefined range is illuminated.Usually, a headlight adjustment is effected in a garage with a headlightadjusting device. It is disadvantageous with this method that aheadlight adjustment is combined with time and costs for the vehicleowner.

It is, therefore, the object of the present invention to indicate amethod for automatically detecting misalignment of the headlight.

For this purpose a method is indicated with a camera system, which isarranged in or on the vehicle and is oriented on a range in front of thevehicle. Preferably, the camera system is used moreover for theembodiment of a driver assistance system. The camera system detects thecurrent beam characteristic depending on the position of a vehicleheadlight. The position of the headlight is indicated e.g. by the pitchand yaw angle. Besides, a desired characteristic for the headlight beamfor at least one headlight position is known. If there is a differenceto the desired and actual beam characteristic with a predefinedheadlight position a misalignment of the headlight is detected.

The actual beam characteristic is determined in particular duringoperation of the vehicle on a free road. If no objects are detected onthe roadway in front of the vehicle, then with a predefined headlightadjustment, e.g. idle state=zero degree (i.e. yaw angle=zero degree andpitch angle=0 degree), the light intensity visible in the camera pictureis determined. In an advantageous embodiment of the invention a rangewith an intensity above a predefined threshold value is determined, ase.g. not the entire illumination range of the headlight is recorded bythe camera system. For increasing the measurement accuracy it isadvantageous to combine several measurements and to average, ifnecessary.

In an advantageous embodiment of the invention the position of theactual light distribution pattern is evaluated with regard to a surfaceparallel to the vehicle longitudinal axis, in particular the lane of thevehicle. This method offers the advantage that the adjustment of aheadlight can be tested during the vehicle operation. In particular, themethod is applied with a free roadway, if no objects are detected on theroadway. With a predefined headlight position the light distributionpattern on the roadway is detected and is compared with a desired lightdistribution pattern which considers the picture of the lightdistribution pattern on a surface parallel to the roadway.

Alternatively, the actual light distribution can also be determined byobserving the local brightness on the basis of retro-reflective objects.Retro-reflective objects are frequently used to identify the roadwaylimitation. Methods are known in the image processing, with the aid ofwhich the location of an object can be estimated on the basis of imagedata of a mono and/or stereo camera. The brightness of retro-reflectiveobjects in the image is proportional to the actual light irradiation atthe location of the object. If necessary, with this method also thetemporal brightness process of an object is considered in a picturesequence. With the known true speed of the vehicle and a localestimation for the retro-reflective objects in this way the actual lightdistribution pattern can be measured. This method is particularlysuitable, if the light distribution pattern cannot be determined on asurface parallel to the roadway.

In a further embodiment of the invention the light distribution patternis evaluated with regard to the lane of the vehicle. With a linear lane,the light distribution pattern of a headlight is symmetrical to thecourse of the lane. Thus, in this embodiment the accurate viewingdirection of the camera system must not be known, if the course of thelane is known in the camera picture. The detection of a lane from imagedata is state of the art and is already implemented in lane keepingsystems.

In a further positive embodiment of the invention the light distributionis determined with regard to the vehicle longitudinal axis, in which atfirst the visual vanishing point of objects is determined in the videopicture (FOE, focus of expansion) during the trip. The visual vanishingpoint results in particular from the movement trajectories of objects,e.g. roadway markings, forthcoming vehicles etc. Objects which are faraway are detected first in the vanishing point or close to it and moveinto other picture areas when approaching. From the position of thevisual vanishing point in the camera picture and if applicable of themovement trajectories of objects in particular when driving straightahead the direction of movement of the vehicle and thus the position ofthe vehicle longitudinal axis can be suggested.

In a further embodiment of the invention the position of the actuallight distribution pattern is recorded, if the vehicle stands in frontof a surface, which is arranged vertical to the vehicle longitudinalaxis. In this case the method for detecting misalignment can beperformed e.g. in front of a house or garage wall. E.g. with astandstill of the vehicle the method can be performed automatically orwhen desired by the driver before the start or after the end of a trip.In a further embodiment of the invention the headlight radiates aspecial light distribution pattern for detecting the misalignment. Inparticular, the light pattern is predefined in such a manner that acentral portion of the headlight darkens and/or light is radiated onlyin a central portion. This central portion is e.g. circular orrectangular.

In a special embodiment of the invention a desired light distributionpattern depending on the form of the actual light distribution patternis selected for a comparison. This is in particular of importance if theactual light distribution pattern is detected on a surface, which can bearranged parallel or vertical to the vehicle longitudinal axis. Forexample, the projection of the actual light distribution is recorded onthe roadway or at a wall vertical to the vehicle longitudinal axis. Thecourse of the actual light distribution is in both cases different andmust, therefore, be compared with different desired light distributionpatterns. In FIG. 1a a typical light distribution pattern is shown whenrecording the roadway and in FIG. 1b when recording a wall vertical tothe vehicle longitudinal axis.

In a preferred embodiment of the invention a warning signal is givenwhen a misalignment is detected to advise the driver of themisalignment. The warning signal can be given optically, acousticallyand/or haptically.

In a further embodiment of the invention a headlight calibration for atleast two predefined headlight positions is performed when amisalignment is detected, so that the actual light distribution complieswith the desired light distribution.

In a further embodiment of the invention a headlight calibration for atleast two predefined headlight positions is automatically performed whena misalignment is detected and a calibration is requested by the driver.The calibration request by the driver can be effected for example by aninput device inside the vehicle.

1. A method for detecting misalignment of a vehicle headlight using acamera system, wherein the headlight is in a predefined position and thecamera system is arranged on or in the vehicle and is oriented in such amanner that the light distribution pattern of the headlight in front ofthe motor vehicle is detected, with a predefined headlight position anactual light distribution pattern of the headlight is recorded using thecamera system and is compared with a desired light distribution patternfor the predefined headlight position, if the actual light distributionpattern differs from the desired light distribution pattern,misalignment of the headlight is detected.
 2. A method according toclaim 1, wherein the actual light distribution pattern is detected onthe basis of the position of an illumination range with an intensityabove a predefined threshold value in the picture.
 3. A method accordingto claim 1, wherein the actual light distribution pattern is detected onthe basis of a brightness of retro-reflective objects in at least onepicture. 4-12. (canceled)
 13. A method according to claim 1, wherein theposition of the actual light distribution pattern is evaluated withregard to a surface parallel to the vehicle longitudinal axis, inparticular the lane of the vehicle.
 14. A method according to claim 1,wherein the position of the actual light distribution pattern isevaluated with regard to a visual vanishing point in the video picture.15. A method according to claim 1, wherein the position of the actuallight distribution pattern is recorded, if the vehicle stands in frontof a surface, which is arranged vertical to the vehicle longitudinalaxis.
 16. A method according to claim 1, wherein the headlight fordetecting the misalignment radiates a special light distributionpattern.
 17. A method according to claim 1, wherein for a comparison adesired light distribution pattern is selected depending on the form ofthe actual light distribution pattern.
 18. A method according to claim1, wherein a warning signal is given when a misalignment is detected.19. A method according to claim 1, wherein a headlight calibration isperformed for at least two predefined headlight positions when amisalignment is detected.
 20. A method according to claim 1, wherein aheadlight calibration is performed for at least two predefined headlightpositions when a misalignment is detected and a calibration is requestedby the driver.
 21. A vehicle with a device for detecting misalignment ofa headlight, comprising a controllable headlight with a control device acamera system, which is arranged on or in the vehicle and is oriented insuch a manner that a light distribution pattern of the headlight infront of the motor vehicle is detected, and an evaluation unit, which isconnected with the control device of the headlight and the camerasystem, and which stores a program for executing a method for detectinga misalignment of the vehicle headlight using the camera system, whereinthe headlight is in a predefined position and the camera system isarranged on or in the vehicle and is oriented in such a manner that thelight distribution pattern of the headlight in front of the motorvehicle is detected, wherein with a predefined headlight position anactual light distribution pattern of the headlight is recorded using thecamera system and is compared with a desired light distribution patternfor the predefined headlight position, and wherein if the actual lightdistribution pattern differs from the desired light distributionpattern, then a misalignment of the headlight is detected.